The present invention relates to a pneumatic vacuum generator.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Different kinds of vacuum generators are used to produce a negative pressure. In the field of automation, vacuum generators are used which generate a negative pressure using the Venturi principle. These vacuum generators are also called ejectors and require compressed air for building up the negative pressure. Prior art ejectors with cylindrical venturi nozzles or multistage ejectors with cylindrical venturi nozzles have been in use for some time. Also known are cylindrical transport ejectors that operate according to the Coanda principle and the planar Coanda principle.
U.S. Pat. No. 6,394,760 describes a multistage ejector, shown in more detail in FIG. 1a-1d and designated by reference numeral 10. The multistage ejector 10 has four suction stages 12, 14, 16, 18 with cylindrical venturi nozzles 20 to 26. FIGS. 1a-1d show schematically, in four cross-sectional views, the ejector 10 at gradually increased vacuum levels in a vacuum chamber 28 and overall decreasing vacuum flow. In FIG. 1a the ejector 10 is shown in a mode of operation in which compressed air is introduced in a direction of arrow 30 into the first venturi nozzle 20 so that air is drawn from the vacuum chamber 28 in a direction of arrow 32. Compressed air flows also through the venturi nozzle 22 so that air is drawn in a direction of arrow 34. The same happens also with respect to the venturi nozzles 24, 26 so that air is drawn in a direction of arrows 36, 38, respectively. Compressed air exits the multistage ejector 10 together with the aspirated air in a direction of arrow 40 through port 42. The total amount of suction air (arrows 44) enters the multistage ejector 10 via port 46. Flap valves 48, 50, 52 in the suction stages 14, 16, 18 are all open. As a result, the vacuum flow is high. FIG. 1b shows the multistage ejector 10 in an operating position in which the flap valve 52 is closed. When a particular negative pressure has been reached in the vacuum chamber 28, the flap valve 52 closes spontaneously so that suction air is drawn only via the suction stages 12, 14, 16 in the direction of arrows 32, 34, 36, respectively. As a result, the vacuum flow decreases while the negative pressure in the vacuum chamber increases. FIG. 1c shows the multistage ejector 10 in an operating position in which the flap valve 50 is closed as a result of the still higher negative pressure has been reached in the vacuum chamber 28. Thus, air is drawn only via the suction stages 12, 14 in the direction of arrows 32, 34, respectively. In FIG. 1d, also flap valve 48 closes as a result of a still higher negative pressure in the vacuum chamber 28, i.e. all flap valves 48, 50, 52 are now closed. Air is now drawn solely via the suction stage 12 in the direction of arrow 32. The vacuum flow is thus further decreased, indicated by the lesser number of arrows. On the other hand, a maximum negative pressure is generated in the vacuum chamber 28.
FIG. 2 shows a conventional multistage ejector 10a with three suction stages 12, 14, 16 and two flap valves 48, 50 which assume their closed positions. Parts corresponding with those in FIG. 1 are denoted by identical reference numerals and not explained again. Compressed air is introduced via two ports 54, whereas outgoing air exits through two ports 42 and one port 56, as indicated by the arrows. The mode of operation corresponds to the multistage ejector 10, as described with reference to FIGS. 1a-1d. 
FIGS. 3a and 3b show by way of example a conventional Coanda ejector as disclosed in International application WO 2009/054732 A1 and designated by reference numeral 58. The Coanda ejector 58 is made in sandwich construction and includes a top plate 60, a bottom plate 62, and an intermediate plate 64. In FIG. 3a, the Coanda ejector 58 is of single-stage configuration, whereas in FIG. 3b, the Coanda ejector 58 has several parallel stages. In FIG. 3a, compressed air enters through port 54 in a direction of arrow 30 into the Coanda ejector 58 and is introduced tangentially via a channel 65 into a chamber 66. As a result, air is drawn in a direction of arrows 44 through a perforated inlet 46 in the bottom plate 62 and exits the chamber 66 together with compressed air via outlet channel 67. In the variation of FIG. 3b, compressed air is dispersed via a manifold 68 to several channels 65. Thus, compressed air is split over a total of six chambers 66. The bottom plate 62 has thus six inlets 46 to enable a gripping of a workpiece 70 over a large area.
A drawback common to all prior art vacuum generators or ejectors is their bulkiness.
It would therefore be desirable and advantageous to address this problem and to obviate other prior art shortcomings.